A Combined Effect of the Earth's Magnetic Dipole Tilt and IMF By in Controlling Auroral Electron Precipitation

Abstract Auroral particle precipitation is usually assumed to be equally strong for both signs of the B y component of the interplanetary magnetic field (IMF). This is also the case in most currently used precipitation models, which parameterize solar wind driving by empirical coupling functions. However, recent studies have showed that geomagnetic activity is significantly modulated by the signs and amplitudes of IMF B y and the Earth's dipole tilt angle Ψ. This so called explicit B y dependence is not yet included in any current precipitation models. In this paper, we quantify this B y dependence for auroral electron precipitation for the first time. We use precipitation measurements of the Defense Meteorological Satellite Program (DMSP) Special Sensor J instruments from years 1995–2022. We show that the dawnside electron precipitation at energies 13.9–30 keV is greater at auroral latitudes for opposite signs of B y and Ψ in both hemispheres, while the dusk sector is mostly unaffected by B y and Ψ. For energies below 6.5 keV the B y dependence is strong poleward of the auroral oval in the summer hemisphere, also exhibiting a strong dawn‐dusk asymmetry. We also show that B y dependence of precipitation modulates ionospheric conductance.